This invention relates to power transmission belts and to a rubber composition for use therein.
Continually increasing temperatures in the engine compartment of motor vehicles has resulted in conventional compounds such as neoprene becoming obsolete due to insufficient heat resistance. In many instances, a change has been made to hydrogenated nitrile butadiene rubber (HNBR). However, HNBR is a very expensive rubber. See e.g. U.S. Pat. No. 5,599,246. More recently, the use of alkylated chlorosulfonated polyethylene (ACSM) has been suggested as a lower cost alternative to HNBR. See e.g. U.S. Pat. No. 5,711,734; 5,408,007 and 5,626,953. While ACSM polymer suffer some deficiencies, such as retention of properties at elevated temperatures and oil resistance, when used by itself, we have found that blending the ACSM with ethylene vinyl acetate (EVM and curing the blends with an organic peroxide and a cure co-agent overcome those deficiencies.
U.S. Pat. No. 5,322,479 relates to a transmission belt comprising an alkylated chlorosulfonated ethylene-alpha-olefin copolymer (ACSM) matrix elastomer compound or a non-alkylated chlorosulfonated ethylene-alpha-olefin copolymer (CSM) matrix elastomers compound in addition to a hydrogenated butadiene-acrylonitrile copolymer matrix elastomer compound.
French Pat. No. 2,628,678 discloses the use of chlorosulfonated ethylene-alpha-olefin copolymer (CSM) matrix compounds for constructing belts. It, however, was noted in U.S. Pat. No. 5,322,479 that although the belts made with CSM exhibit a positive increase of operational characteristics at higher temperatures, such belts retain a sensitivity to oils which thereby reduces their performance in case of accidental contact with oil.
U.S. Pat. No. 4,180,531 discloses a method of promoting peroxide initiated crosslinking of CSM whereby the solubility of peroxide vulcanizing agents is increased. Increased peroxide solubility and/or processability is accomplished by blending ethylene vinyl acetate with CSM.
In accordance with the practice of present invention, there is provided a rubber composition comprising:
a. from 90 to 10 parts by weight per 100 parts of rubber (phr) of ACSM;
b. from 10 to 90 phr of EVM;
c. from 20 to 75 phr of carbon black; and
d. from 2 to 10 phr of an organic peroxide.
There is also disclosed a power transmission belt produced from a rubber composition comprising:
a. from 90 to 10 phr of ACSM; and
b. from 10 to 90 phr of EVM.